The exception to this is cars that are calibrated for a range of fuels and can safely run on less than ideal fuels. This is similar to the difference between 93 recommended and 93 required.
87 or higher means that the car will run just fine on higher than 87 octane fuels, but it should not be run with lower than 87 octane fuels. If the car had a performance increase with 93 octane fuels, the manufacturer would state "93 octane recommended" so that the engine will run at it's peak performance (and likely last longer) with the recommended fuel, but may be safely operated with fuels rated less than 93 at the expense of performance.